This invention relates generally to manufacturing tobacco sheet material and, more particularly, to an apparatus and method for the continuous sheet casting of tobacco sheet material.
One method for manufacturing tobacco sheet material is illustrated in the block diagram of FIG. 1. Tobacco stems 10 are washed 12, reduced to an appropriate size 14 (e.g., 12-400 mesh) and blended to be homogenous 16. Tobacco dust 18 is likewise reduced to an appropriate size 20 (e.g., 12-400 mesh) and blended to be homogenous 22. Then, these sized tobacco components are mixed together and mixed with an appropriate extract solution 24 to produce a slurry 26. The extract solution 24 facilitates extraction of pectin chemically bound in the tobacco components.
The next step in this process is time consuming: the slurry 26 must age for at least three to four hours 28. During the aging step 28, two changes in the slurry 26 take place which are essential to the subsequent casting of tobacco sheet material from slurry. First, pectin is extracted from the tobacco components and released into the slurry 26. Inclusion of pectin in the slurry 26 is necessary for bonding of the tobacco components into sheet material. Second, the slurry 26 absorbs fluid. This is commonly referred to as wetting. Sufficient wetting is necessary to form tobacco sheet material which is pliant and not brittle. Typically, the slurry 26 is pumped into a storage tank to age.
After the slurry has aged for approximately three to four hours 28, the manufacturing process continues. The slurry is first refined to further reduce the size of the tobacco components 30 and then the slurry is cast in conventional fashion to form tobacco sheet material. The casting process involves forming 32 and drying 34 the slurry.
Due to the long aging step 28, this method of manufacturing tobacco sheet material requires precise advanced planning. The need for tobacco sheet material must be accurately estimated more than three hours in advance. In addition, manufacturing must be timely scheduled so that fabrication and cleanup can be completed within scheduled work shifts.
To reduce or eliminate the long aging step, two other methods for manufacturing tobacco sheet material have been developed. The first method substitutes a binder solution for the extract solution 24. By adding binder to the slurry, the need to wait for natural pectin to be released from the tobacco components is eliminated. Such binder solutions may include adhesive or pectin obtained from an external source. Extrinsic pectin may be obtained from non-tobacco products. Examples of this approach are U.S. Pat. Nos. 4,164,948, 4,325,391, 4,337,783 and 4,702,264 and Canadian Pat. No. 1,116,970.
Adhesive or extrinsic pectin added to the slurrY is not chemically equal to pectin extracted from tobacco components in the slurry. Accordingly, tobacco sheet material manufactured with a binder solution is less natural than tobacco sheet material manufactured using an extract solution.
The second alternative method substitutes a high intensity mechanical mixer for the aging step. The high intensity mechanical mixer, in combination with an extract solution, quickly releases pectin from the tobacco components into the slurry. The mechanical mixer uses high shear mixing to extract the pectin. Wetting of the slurry takes place during the high shear mixing. Mechanical high shear mixing is energy intensive and reduces the size of the tobacco components. U.S. Pat. No. 4,674,519 discloses this method.